254 
BRITISH ENTOMOSTRACA. 
The natatory feet are very imperfectly developed ; their 
function being supplied by two pairs of organs in form of 
rami, placed on the anterior part of the body. The first pair 
corresponds with the antenna in the perfect animal ; the 
antenna itself being well developed, and the appendage 
which projects from its posterior edge being enlarged into 
this ]ong ramus, constituting the chief part of the organ. 
The second pair corresponds with the first pair of foot-jaws 
in the adult. These organs are large, consisting of several 
articulations, the terminal one of which gives off several 
long setae. By means of these rami the little creature 
moves with ease by bounds, like the Daphnia. The 
sucking-discs are not yet formed, their place being sup- 
plied by a pair of large feet, broad at their base, and ter- 
minating in a prehensile hook, by means of which the 
animal can fix itself upon its prey. The organs imme- 
diately following these are only slightly developed, and 
correspond with the third pair of foot-jaws, and the nata- 
tory feet are little more than rudimentary. In this state 
the young animal continues for about six days, when it 
casts its shell. Three days after the first moult, it changes 
its shell again ; and two days after that a third moult 
takes place. By this time we find the rami have dis- 
appeared, the natatory legs have become developed, and 
the sucking- discs have assumed somewhat of their shape 
and appearance. 
Two days after this the fourth change of shell takes 
place, when the sucking-disc has become perfect. Six 
days later, the fifth moult occurs, when the sexual organs 
make their appearance ; and after the sixth change, which 
takes place six days subsequently, or twenty-five days 
from their being hatched, the animals commence to breed. 
They have now, however, only attained half their full 
growth, but gradually augment in size after successive 
moults, which take place every six or seven days. 
An experiment conducted by Jurine, and fully detailed 
by him, tends to prove that the Arguli do not, like some 
of the Branchiopoda, become pregnant without the inter- 
